Lexel 88 problems - Help please

[smogthemog]

Did some more work with it last night and found one of the transistors on the PB to be short. I guess this popped when I tried it and it faulted the same as it did before.

After replacement, I now have the PB back working using the 12v supply and a battery/10k pot method.

I get the 34v REG voltage still when I switch everything on to go but it disappears when I plug in the CPC. I guess this is correct.

With the head still disconnected, is there ANY way of checking the operation of the CPC and PB whilst in circuit and running at HV?

If i put my voltage meter between -HV and the base of the small driver transistor and turn the current control on the front of the PSU I get around 1.8v constant reguardless of where the pot turned. Pot seems OK when checked.

I have a ALC60 sat here..... Could it be used to test the PSU?

Jim

[mixedgas]

Oscillation noise in the ignitor ? 50 hz ? is the signal to the ignitor relay AC or DC? (most were DC.. A few later ones were AC)

Pop the cover on the ignitor and shoot me a picture.. Are there 2 metal caps in the ignitor?

Nothing should oscillate in the ignitor and NO ONE EXPECTS THE SPANISH INQUISITION!

You just may be the first bad ignitor EVER!

Steve

[smogthemog]

Oscillation noise in the ignitor ? 50 hz ? is the signal to the ignitor relay AC or DC? (most were DC.. A few later ones were AC)

Pop the cover on the ignitor and shoot me a picture.. Are there 2 metal caps in the ignitor?

Nothing should oscillate in the ignitor and NO ONE EXPECTS THE SPANISH INQUISITION!

You just may be the first bad ignitor EVER!

Steve

Oscillation noise is from the igniter and it sounds to be 50Hz.
Igniter coil is 120vAC 50/60Hz.
No cover on the igniter.
There are 2x metal caps and an 11W 32K resistor and they have all been tested OK.
I have also tested the other Cap and resistor under the expansion chamber and they are both OK too.

I haven't run it up since replacing the crimp connectors - I was hoping of a full PB/CPC test procedure without the head connected??

Thanks again for your help.

[mixedgas]

testing it in working order with power involves buying 1.5 KW electric water heater elements, which are about 20$ US each. It sounds like you have the wrong ignitor relay (dc in ac, ac in dc,) or a stuck ignitor button.

Steve

[smogthemog]

Where do they need to be in cct Steve? I have several fan heaters here of around 2200W or so?

The noise comes from the igniter coil not the relay. The relay operates fine and springs back OK when the fire button is released.

I have tried it again tonight and blew 3 transistors in the PB. It did exactly the same as before. Lots of Noise and ran at full current

I am going to replace the transistors and then fully check the umbilical and Amphenol plug for breakages/shorts.

I will then, pending some help with connections, try the fan heater idea.
Do I need to connect anything to the magnet output feed from the PSU?
I am guessing the

I have a 50ohm oil cooled 100W dummy load which I could use if need be?

[mixedgas]

OK, something is wrong, most likely in the head wiring or umbilical,in a rare case, the magnet. For a passbank to blow like that, its getting direct rectified line at some point.

Do you have access to a "megger" for checking for breakdown in cabling?

Or a improvised megger,, some sort of HV power supply and a neon lamp etc??

1. Last time I saw this sort of thing it was a insulation breakdown.


It is highly unlikely that a lexel tube would be so low in pressure to oscillate or "thyratron" and yet start that easy.
If this were a coherent I'd say super low tube pressure, below the inversion point. But this is a long positive column laser and they usually cant get that low. How many hours on this beast? Not that the hour meter is in the least accurate, nor are they replaced if the tube is ever changed.


2. you dont need the magnet hooked in for a resistive load test.

3. the load resistor goes from pin "P" which is the anode to regulated -HV which is either of the cathode leads.

4. make sure the tube anode is clearly far away from the magnet and the anode lead is not arcing over to ground.

If this ends up being in the ignitor or other exotic part, dont worry, I have quite a scrap pile.

Other then the fact that 2200 watt heaters are highly inductive, I see no issue for using them as a test load.

I'd also get on the horn to Mr Bohen's tech at the factory, and tell him what your symptoms are and what you have done so far, email would work.

I'll call him tomorrow and ask if they have any ideas besides what I can suggest.

Steve

[smogthemog]

I don't have a Megger but I can sort a HV supply and neon, no problem.

I will do a full insulation check of the umbilical, plug & anything else I can find before I go any further.

I have also ordered 10x more 2N6259 so that I can match the ones I already have in the PB to the new ones and come up with 12x matched transistors.

Does it matter Steve which leg of the filament wires (-HV & cathode (unregulated)) I connect to the other end of the resistive load? P1-X or P1-W????

Am I correct in the assumption that the HV unregulated DC (+180VDC'ish) connects to the magnet and the 20-60v regulated DC (via the CPC & PB combo) connects to the Anode and Cathode of the tube?

I don't quite understand what voltage is where in the head

Once explained to me, things always become obvious but i can stare all day at pictures and writing on paper and it just wont click All part of my A.D.D I guess.

[smogthemog]

Out of interest Steve, what sort of wonga will you be looking at, for that spare tube you have?

[smogthemog]

Does anyone have a spare Light control photocell mount for the end of this laser aperture?
Not the actual photocell, just the plastic mount that it fits into - mine is not there
Pic below:


I am in the midst of completely stripping the head down and cleaning and checking everything and I also removed all the cables from each umbilical to check their integrity. All is OK with them. They where a right git to get back in!

There are certainly signs of slight water ingress within the head area, especially under where the flexi water pipes join the tube, but no signs of arcing anywhere as far as I can see.
I have checked, with my Fluke multimeter set to Mohms, between earth and all the cables from the laser tube. All seems OK. I haven't yet tried the megger test with them.

I have visually checked the igniter and with it being of very simple design and the fact you can see most of it quite easily, I don't think there is anything wrong with it but I can't be sure. Caps, Relay and resistor are OK. I am going to give it a good coat of anti-corona spray before it all goes back together, omitting the relay contacts of course

Do you have one at your end Steve that you can check the Resistances for me please?


Will you be at our LEM Steve?

[mixedgas]

I talked with my best friend who bought the Lexel factory auction stuff a few years ago. A 85SVG, tube, speced for well in excess of a watt would be 500$ and shipping. But I'm not entirely convinced its the tube. Smog, do you have skype access? I could not easily afford a international phone call, but skype might be a way to go... You really need a test load, even if its 10 x 100 watt 220V light bulbs

Steve